Continuous production of esters of glycols or their monoethers with lower fatty acids

ABSTRACT

Continuous production of substantially or wholly water-soluble esters of glycols or their monoethers with lower fatty acids by reaction of a glycol of the formula (I): HO-A-X (I) in which A is ethylene, propylene or butylene; and X is OH or OR in which R is alkyl of one to four carbon atoms or OAOH or OAOR in which A and R have the meanings given above with a lower saturated fatty acid at elevated temperature in the presence of a catalytic amount of a strong acid while continuously removing the water formed by means of an entrainer followed by treatment with an aqueous alkali. The glycol of the formula (I) is reacted in a first zone with the lower fatty acid, the water formed being distilled off as an azeotrope over the top by means of an entrainer, and the crude glycol ester including the entrainer is removed from the bottoms, mixes with an aqueous alkali, extracted in a second zone while supplying an extractant and water with phase separation and in a third zone the pure glycol ester is recovered from the resulting mixture of glycol ester, entrainer and extractant by rectification. Glycol esters are used as solvents for surface coating agents.

United States Patent 1 Hohenschutz et al.

[ 1 Dec.2, 1975 1 CONTINUOUS PRODUCTION OF ESTERS OF GLYCOLS OR THEIR MONOETHERS WITH LOWER FATTY ACIDS [73] Assignee: Badische Anilin- & Soda-Fabrik Aktiengesellschaft, Ludwigshafen (Rhine), Germany [22] Filed: June 6, 1973 [21] Appl. No.: 367,327

[30] Foreign Application Priority Data June 10, 1972 Germany 2228335 [52] U.S. Cl. 260/496; 260/488 .1; 260/499 [51] Int. C1. C07C 67/08 [58] Field of Search 260/488 J, 496, 499

[56] References Cited UNITED STATES PATENTS 1,972,579 9/1934 Wickert 260/488 J 2,757,157 7/1956 Hetzel 260/488 J 2,871,248 1/1959 Kirkland et a1. 260/488 J 2,920,056 1/1960 Banes et a1 260/488 J 3,023,185 2/1962 Bartlett et al. 260/488 J 3,053,883 9/1962 Dean et a1 260/488 J Primary Examiner-Vivian Garner Attorney, Agent, or Firm-Johnston, Keil, Thompson & Shurtleff [57] ABSTRACT Continuous production of substantially or wholly water-soluble esters of glycols or their monoethers with lower fatty acids by reaction of a glycol of the formula (1):

HOA-X (l) in which A is ethylene, propylene or butylene; and X is OH or OR in which R is alkyl of one to four carbon atoms or OAOH or OAOR in which A and R have the meanings given above with a lower saturated fatty acid at elevated temperature in the presence of a catalytic amount of a strong acid while continuously removing the water formed by means of an entrainer followed by treatment with an aqueous alkali. The glycol of the formula (1) is reacted in a first zone with the lower fatty acid, the water formed being distilled off as an azeotrope over the top by means of an entrainer. and the crude glycol ester including the entrainer is removed from the bottoms, mixes with an aqueous alkali, extracted in a second zone while supplying an extractant and water with phase "separation and in a third zone the pure glycol ester is recovered from the resulting mixture of glycol ester. entrainer and extractant by rectification. Glycol esters are used as solvents for surface coating agents.

10 Claims, I bl-swin Figure CONTINUOUS PRODUCTION OF ESTERS OF GLYCOLS R THEIR MONOETI-IERS WITH LOWER FATTY ACIDS This invention relates to an improved continuous process for the production of wholly or substantially water-soluble esters of glycols or their monoethers with lower fatty acids.

It is known that carboxylic esters are obtained by heating mixtures of carboxylic acids and alcohols in the presence of strong acids as catalysts and continuously removing the water formed (compare Houben-Weyl, Methoden der organischen Chemie, volume 8, 1952, pages 516 et seq.). The crude carboxylic esters are worked up as a rule by neutralization with aqueous alkalies followed by distillation. This procedure cannot be carried out in the production of wholly or partly water-soluble esters, for example in the case of esters of lower glycols or glycol alkyl ethers because in the treatment with aqueous alkalies considerable quantities of useful products pass into the waste water. Solid neutralization agents which are insoluble in the ester are therefore usually employed and this has the disadvantage that encrustation of the evaporator takes place in the subsequent distillation. In a method described in German Pat. No. 975,700 washing with aqueous alkalies is dispensed with and the useful products are distilled from the reaction mixture containing acid. This method has the disadvantage that apparatus used for the purifying distillation of the glycol esters is corroded.

It is an object of the invention to provide a process in which encrustation and corrosion do not occur in the distillation of the pure ester. Another object of the invention is to provide a process in which useful watersoluble products are not discharged in the effluent.

In accordance with this invention these and other 013- jects and advantages are achieved in an improved process for the continuous production of wholly or substantially water-soluble esters of glycols or their monoethers with lower fatty acids by reaction of a glycol of the formula (I):

HO-A-X in which A is ethylene, propylene or butylene and X is OH or OR in which R is alkyl of one to four carbon atoms, or OAOH orOAOR in which A and R have the above meanings, witha lower saturated fatty acid at elevated temperature in the presence of a catalytic amount of a strong acid with continuous removal of water by entrainment followed by treatment with an aqueous alkali, wherein the improvement consists in reacting the glycol of the formula (I) with the lower fatty acid in a first zone in which the water formed is distilled azeotropically by means of an entrainer over the top and the crude glycol ester including entrainer is withdrawn from the bottoms, adding aqueous alkali, extracting the ester in a second zone with the supply of extractant and water with phase separation, and recovering the pure glycol ester by rectification of the resulting mixture of glycol ester, entrainer and extractant in a third zone.

There is accordingly the problem of preparing watersoluble glycol esters of lower fatty acids without encrustation or corrosion occurring during the distillation and moreover of preventing discharge of useful products with the effluent.

We have now found that wholly or substantially water-soluble esters of glycols or their monoethers with lower fatty acids are obtained more advantageously than hitherto in a continuous process involving the reaction of a glycol of the formula (I):

HO-AX in which A is ethylene, propylene or butylene and X is OH, OR where R is alkyl of one to four carbon atoms, OAOH or OAOR where A and R have the above meanings with a lower fatty acid at elevated temperature in the presence of a catalytic amount of a strong acid with continuous removal of the water formed by means of an entrainer followed by treatment with an aqueous alkali, when in a first zone the glycol of the formula (I) is reacted with the lower fatty acid in the presence of a catalytic amount of a strong acid, the water formed being simultaneously distilled off over the top by means of an entrainer and the crude glycol ester including the entrainer being withdrawn from the bottoms, the ester is mixed with an aqueous alkali and extracted in a second zone while supplying extractant and water with phase separation, and in a third zone the pure glycol ester is recovered by rectification from the mixture of glycol ester, entrainer and extractant.

The new process has the advantage that encrustation and corrosion phenomena do not occur in the distillation of the pure ester. Moreover the new process has the advantage that useful products are not discharged with the effluent.

Examples of preferred glycols of the formula (I) are ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether and diethylene glycol monomethyl ether. Starting materials of the formula (I) which have been derived from ethylene glycol and propylene glycol, particularly ethylene glycol, have special significance and among them particularly the C to C alkyl ethers.

Lower fatty acids of one to four carbon atoms such as formic acid, acetic acid, propionic acid and butyric acid are preferred.

The glycol of formula (I) and the lower saturated fatty acid are generally used in stoichiometric ratio. An excess of glycol of up to preferably 5 percent by weight may be used.

The reaction is carried out in a first zone in the presence of a catalytic amount of a strong acid, the water formed being taken overhead by means of an entrainer. Suitable entrainers are those which form an azeotrope with water out not with the glycol esters. The boiling point of the entrainer used should be as far as possible below that of the ester to be prepared. Example of suitable entrainers are hydrocarbons such as benzene or toluene. Esters of alkanols of one to five carbon atoms with fatty acids of one to four carbon atoms, particularly acetic acid, such as ethyl, propyl, butyl and pentyl acetate, are preferred. The entrainer is conveniently used in an amount of from 20 to percent by weight based on the crude ester.

The reaction is carried out in the presence of a strong acid present in a catalytic amount. It is preferred to use non-oxidizing strong mineral acids such as hydrochloric acid, sulfuric acid, phosphoric acid or organic sulfonic acids such as benzenesulfonic acid or toluenesulfonic acid. The said acids are advantageouslyused in amounts of from 0.1 to 2 percent and particularly from 0.5 to 1.5 percent by weight based on the mixture of glycols and lower fatty acids.

The first zone may conveniently be a rectifying zone. Conventional rectifying columns may advantageously be used for the purpose. Packed columns or plate columns have proved to be particularly suitable. The columns used advantageously have from to 35 theoretical plates.

The temperature in the bottoms is kept as a rule at from 130 to 160C, while the top temperature is adjusted according to the boiling point of the entrainer used.

After the water has been separated it is advantageous to return the entrainer to the top of the column so that a mixture of crude glycol ester and entrainer is withdrawn from the bottoms. Naturally the ratio of crude glycol ester to entrainer will correspond to the feed ratio given above.

The mixture of crude glycol ester and entrainer obtained is mixed with an aqueous alkali. Examples of suitable alkalies are caustic soda solution, cau'stic potash solution and sodium carbonate solution. The alkali is conveniently used as a 4 to 8 percent by weight solution. it is advantageous to use from 1.2 to 2.0 and particularly from 1.4 to 1.6 times the stoichiometric amount of alkali based on the acid used as catalyst. The crude glycol ester and the aqueous alkali are advantageously mixed in a tubular zone in which intense mixing takes place. The treatment is carried out as a rule at a temperature of from 20 to 60C.

The mixture of aqueous alkali, crude glycol ester and entrainer thus obtained is extracted in a second zone with the supply of an extractant and water with phase separation. The second zone may conveniently be an extractive column, for example a pulse column. The said mixture is advantageously supplied in the middle and water at the top of the column while extractant is introduced in the lower third. The wash water is removed at the lower end. The upper organic phase, which contains crude glycol ester devoid of acid, is taken overhead.

Suitable extractants include hydrocarbons such as benzene or toluene and also esters of alkanols of one to five carbon atoms with fatty acids of one to four carbon atoms and particularly acetates such as ethyl acetate or butyl acetate. It is advantageous for the extractant to have a substantially lower boiling point than the glycol ester to be prepared. it has proved to be particularly convenient for the extractant to be identical with the entrainer. It is advantageous to supply such an amount of the extractant that the organic phase removed contains from 30 to 170 percent and particularly from 50 to 100 percent of extractant inclusive of entrainer and based on the crude esterjThe extraction is generally carried out at from 20 to 40C.

The amount of wash water used is generally from 5 to 20 percent by weight based on the crude ester.

The pure glycol ester is recovered by rectification in a third zone from the resulting mixture of ester and extractant including entrainer and it is convenient to distil off the extractant and entrainer together with residual water over the top while the pure glycol ester is preferably removed in the lower third of the column. Conventional columns, for example packed columns or plate columns preferably having from to 40 theoretical plates may conveniently be used for the final distillation.

The process of the invention may for example be carried out, as shown in FIG. 1, by supplying glycol at lower fatty acid at 2 and strong mineral acid at 3 through a line 4 to a column K1, while some of the extractant/entrainer is introduced through line 5 into column K1. An azeotrope of water and entrainer is withdrawn at the top of the column through line 16 and is separated in a separator 17 into two phases, the entrainer being returned through line 18 into column Kl while the water passes through line 7 to a mixing chamber 19. Crude glycol ester mixed with the entrainer and extractant is withdrawn from column Kl through line 6.

Aqueous alkali in container 19 is diluted through line 8 with water and supplied through line 9 to the crude glycol ester and the mixture is supplied to extractive column K2 through line 6 already mentioned. Water is supplied through line 10 to the top of extractive column K2, extractant is supplied through line 15 to the lower third, while water is withdrawn at the lower end through line 24. The organic phase forming in the upper portion of extractive column K2 is passed through line 20 into a distillation column K3 where a mixture of extractant/entrainer is withdrawn as an azeotrope with water at the top through line 21; the water is separated in the separator 22 and returned through line 14 into the mixing vessel 19 while the extractantlentrainer is returned through line 23 into column K3 as a reflux, but the major portion is supplied through line 5 again to column K1 and line 15 to extraction column K2. Pure glycol ester is withdrawn through line 12 in the lower third and high boiling point byproducts are withdrawn from the bottoms through line 13.

The glycol esters thus prepared have low acid numbers of from 0.01 to a maximum of 0.1. The content of glycol ester prepared in this way is always more than 99.5 percent by weight. The glycol esters prepared according to the invention are excellent solvents and are suitable inter alia in the processing of polyurethane and nitrocellulose coating agents.

The process of the invention is illustrated in the following Examples. The parts specified are by weight.

EXAMPLE 1 A mixture of 680 parts per hour of acetic acid and 870 parts per hour of ethylene glycol monomethyl ether is metered together with 28.5 parts per hour of sulfuric acid and 1,300 parts per hour of isobutyl acetate (obtained from the pure ester column) into an esterification column. The water is entrained out over the top. The temperature at the top of the column is 93C and in the bottoms it is from to C. The crude ester is neutralized with 620 parts of an 8% sodium carbonate solution and washed in a washing column to which 250 parts per hour of water is fed at the top. The lower part of the wash column serves as the extractive portion into which 700 parts per hour of isobutyl acetate (also withdrawn as a reflux from the pure ester column) is introduced. The neutralized and washed crude ester which contains 60 percent of isobutyl acetate flows into the pure ester column from which 1,295

parts per hour of methyl glycol acetate is withdrawn as EXAMPLE 2 As described in Example 1 a mixture of 415 parts per hour of acetic acid, 840 parts per hour of butyl glycol (ethylene glycol monobutyl ether) and 25.4 parts per hour of sulfuric acid is metered together with 1,000 parts per hour of isobutyl acetate into the esterification column. A temperature of 93C is set up at the top of the column and of 155 to 160C in the bottoms. Neutralization is carried out with 585 parts of 5 percent caustic soda solution. 200 parts per hour of isobutyl acetate is used for extraction and 200 parts of water per hour is passed into the extractive column. The organic phase from the extractive column is passed into the pure ester column and fractionally distilled. The butyl glycol acetate is withdrawn as a vapor from the lower part of the pure ester column at 200 mm Hg and 144C at the rate of 1,110 parts per hour corresponding to a yield of 98.3 percent based on the acetic acid used. The yield based on butyl glycol is 97.4 percent of theory.

EXAMPLE 3 A mixture of 555 parts per hour or propionic acid and 690 parts of ethyl glycol (ethylene glycol monoethyl ether) is esterified as described in Example 1 in the presence of 24.7 parts of sulfuric acid at 150 to 160C. Toluene serves as extractant. 975 parts per hour is returned to the esterification column and 450 parts per hour of toluene into the extractive portion. 1,060 parts per hour of ethyl glycol propionate is withdrawn at 140C and 220 mm Hg from the pure ester column; this is equivalent to a yield of 97.2 percent based on propionic acid. The yield based on ethyl glycol is 96.8 percent of theory.

EXAMPLE 4 450 parts per hour of acetic acid and 910 parts per hour of methyldiethylene glycol (diethylene glycol monomethyl ether) are esterified as described in Example 1 in the presence of 26 parts per hour of sulfuric acid at 160 to 165C. The amount of butyl acetate for the esterification column is 1,300 parts per hour and for the extractive column 640 parts per hour. At 160C and 200 mm Hg 1,185 parts per hour of methyldiethyleneglycol acetate is withdrawn from the pure ester column, equivalent to a yield of 96.8 percent based on acetic acid. The yield based on methyldiethylene glycol is 96.5 percent of theory.

We claim:

1. A process for the continuous production of wholly or substantially water-soluble esters of glycols or of their monoethers with lower fatty acids, which process comprises:

reacting in a first zone a glycol of the formula HOA-X (l).

in which A is ethylene, propylene or butylene, and X is OH, OR, OAOH or OAOR wherein R is alkyl of one to four carbon atoms and A has the above meaning, with a lower saturated fatty acid at an elevated temperature and in the presence of a catalytic amount of a strong acid while the water formed in the reaction is simultaneously distilled off azeotropically over the top by means of an entrainer which forms an azeotrope with water selected from the group consisting of hydrocarbons and lower fatty acid esters of alkanols of l to 5 carbon atoms, said entrainer being continuously introduced into said first zone and the crude glycol ester mixed with entrainer being continuously withdrawn from the bottom of said first zone;

continuously adding aqueous alkali to the crude glycol ester withdrawn from said first zone;

then continuously extracting the crude glycol ester in a second zone to which there is continuously supplied water and additional entrainer as the extractant with phase separation into an aqueous phase and an organic phase;

continuously separating said organic phase from said aqueous phase; and

continuously recovering the pure glycol ester from said organic phase by rectification in a third zone.

2. A process as claimed in claim 1 wherein the glycol used is ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether or diethylene glycol monomethyl ether.

3. A process as claimed in claim 1 wherein the fatty acid reacted with the glycol has one to four carbon atoms.

4. A process as claimed in claim 1 wherein the glycol is used in a stoichiometric ratio up to an excess of 5 percent by weight based on the lower saturated fatty acid used.

5. A process as claimed in claim 1 wherein an ester of an alkanol of one to five carbon atoms with a fatty acid of one to four carbon atoms is used as entrainer.

6. A process as claimed in claim 1 wherein from 20 to percent by weight of entrainer is used based on the amount of crude ester.

7. A process as claimed in claim 1 wherein the treatment with an alkali is carried out at a temperature of from 20 to 60C.

8. A process as claimed in claim 1 wherein the amount of entrainer used for the extraction is such that the organic phase withdrawn contains from 30 to percent of entrainer based on the crude ester.

9. A process as claimed in claim 1 wherein the extraction is carried out at from 20 to 40C.

10. A process as claimed in claim 1 wherein the boiling point of the entrainer is substantially lower than the boiling point of the glycol ester being produced. 

1. A PROCESS FOR THE CONTINUOUS PRODUCTION OF WHOLLY OR SUBSTANTIALLY WATER-SOLUBLE ESTERS OF GLYCOLS OR OF THEIR MONOESTERS WITH LOWER FATTY ACIDS, WHICH PROCESS COMPRISES: REACTING IN A FIRST ZONE A GLYCOL OF THE FORMULA
 2. A process as claimed in claim 1 wherein the glycol used is ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether or diethylene glycol monomethyl ether.
 3. A process as claimed in claim 1 wherein the fatty acid reacted with the glycol has one to four carbon atoms.
 4. A process as claimed in claim 1 wherein the glycol is used in a stoichiometric ratio up to an excess of 5 percent by weight based on the lower saturated fatty acid used.
 5. A process as claimed in claim 1 wherein an ester of an alkanol of one to five carbon atoms with a fatty acid of one to four carbon atoms is used as entrainer.
 6. A process as claimed in claim 1 wherein from 20 to 100 percent by weight of entrainer is used based on the amount of crude ester.
 7. A process as claimed in claim 1 wherein the treatment with an alkali is carried out at a temperature of from 20* to 60*C.
 8. A process as claimed in claim 1 wherein the amount of entrainer used for the extraction is such that the organic phase withdrawn contains from 30 to 170 percent of entrainer based on the crude ester.
 9. A process as claimed in claim 1 wherein the extraction is carried out at from 20* to 40*C.
 10. A process as claimed in claim 1 wherein the boiling point of the entrainer is substantially lower than the boiling point of the glycol ester being produced. 